Common-mode inductance and radiation of edge placed differential traces on printed circuited board

Abstract

With respect to the single-ended trace (track), differential signaling is most advantageous to signal integrity and common-mode radiation level reduction. However, to guarantee the required signal transmission, the two tracks in the differential pair should be perfectly balanced. Edged placement of a differential pair on the PCB causes balance disruption and creates common-mode (CM) currents resulting in an increased electromagnetic interference level. We quantify the CM inductance and radiation from differential tracks with edge placement. The common-mode inductance of an edged-placed differential pair on a PCB is derived. Then the characteristics of the common-mode inductance of a differential pair are studied for different geometries. Finally, the total radiation powers for several geometries due to the edge placement of the differential pair are measured.